This invention relates generally to polymeric cover slip materials useful for storing biological specimens for a prolonged period of time. In particular, the cover slip material contains a bonding layer that, when activated with a solvent, exhibits adhesive properties and seals the specimen for later use.
In the biological disciplines such as histology or microbiology, it is a common practice to examine a specimen, such as tissue samples, using a microscope, such as a light microscope. Such a practice requires mounting the specimen on a slide, typically a glass slide. A cover slip can be used to protect the specimen and microscope lens. Thin light transmissible glass slides have been used as cover slips. The disadvantage with using glass slides is that they typically cannot preserve the specimen, are fragile, and thus susceptible to fracture thereby possibly damaging the specimen and injuring the user.
In the case where the specimen needs to be preserved for later examination and viewing, some skilled in the art have sealed the cover slip to the slide. For example, U.S. Pat. No. 4,853,262 (Horie et al.) discloses cover film for use in microscopy. The film comprises a plastic substrate and a polymer adhesive disposed thereon. The adhesive is a blend of a first polymer adhesive, having a Tg of at least 80xc2x0 C. (176xc2x0 F.), and a second polymer adhesive, having a Tg of at least 50xc2x0 C. (122xc2x0 F.). The first and second adhesives are different and they can be selected from the group consisting of acrylic adhesive and acrylic copolymer of alkyl methacrylate and alkyl acrylate. The polymer adhesive preferably dissolves or at least swells in an organic solvent, such as xylene.
Others skilled in the art have explored different methods of providing a sealing agent that can be activated in an applying machine, or at the time the cover slip is applied to the slide, by application of a solvent. See, e.g., U.S. Pat. Nos. 4,455,188; 4,188,246; and 3,939,019.
U.S. Pat. No. 3,891,327 (Welch) discloses a method of securing specimen between a cover glass and a glass slide. The method involves (1) covering the glass slide in the region of the specimen with a liquid photosensitive composition consisting essentially of an optically transparent liquid photosensitive material and a photoinitiator, (2) positioning the cover glass over the specimen in contact with the photosensitive composition, and (3) exposing the photosensitive composition to ultraviolet radiation. This process yields a sample where the cover glass and the specimen are in a fixed position on the glass slide. A useful photosensitive composition consists essentially of an acrylate, methacrylate or mixtures thereof and a photoinitiator.
WO 99/53357 discloses a combination comprising (1) a slide suitable for optical microscopy to which a specimen has been applied, and (2) an optically transparent cover adhered to the slide over the specimen. The cover comprises an optically transparent polymeric film with opposite first and second major surfaces, and a contact responsive adhesive on the first major surface, which is in contact with the slide. In some embodiments of the invention, a wetting agent can be applied to the cover or the specimen before the cover is adhered to the slide to improve viewing of the specimen. The contact responsive adhesive is described as pressure sensitive adhesive that adheres relatively quickly and strongly to the target surface yet exhibits essentially no surface tack to the skin when coated on the optically transparent polymeric film.
While the foregoing cover slips are useful, other cover slip compositions are sought.
The present invention provides for a new and improved cover slip material. The inventive cover slip materials possess desirable features, such as clarity, refractive index similar to that of the slide, quick interaction with the activating solvents, compatibility with the staining chemicals used on specimens, and improved stability to high temperature, high humidity conditions for prolonged periods of time.
In one aspect, the invention provides for a flexible, light transmissible cover slip comprising or consisting essentially of (a) a light transmissible polymeric backing having first and second surfaces; (b) a tack free bonding layer disposed on the first surface of the backing, the bonding layer comprising polymers selected from the group consisting of alkyl acrylate, alkyl methacrylate, and combinations thereof; and (c) a protective coating disposed on the second surface of the backing.
In another aspect, the invention provides a method for preparing an optical microscopy slide comprising (a) placing a specimen on a slide, (2) covering the specimen with a flexible cover slip comprising (i) an optically transparent polymeric backing having first and second surfaces; (ii) a substantially tack free bonding layer disposed on the first surface of the backing, the bonding layer comprising polymers selected from the group consisting of alkyl acrylate, alkyl methacrylate, and combinations thereof, (iii) a protective coating disposed on the second surface of the backing; and (3) applying an activating solvent to the bonding layer, wherein upon exposure to the activating agent, at least a portion of the bonding layer is dissolved and the cover slip adheres to the specimen and the microscope slide to yield a prepared slide.
The present invention is unlike the invention disclosed in WO 99/53357 in several respects. First, whereas WO 99/53357 may use a wetting agent on the cover or the specimen before the cover is adhered to the slide to improve viewing of the specimen, the present invention uses an activating solvent to at least partially solvate the bonding layer to impart pressure sensitive adhesive properties. Second, the adhesive system disclosed in WO 99/53357 is described as being contact responsive adhesives and are pressure sensitive adhesives. Such adhesives are described as capable of adhering relatively quickly and strongly to the target surface, i.e., the slide and specimen mounted thereon. The present invention, on the other hand, uses a solvent to activate the bonding layer so as to impart to it adhesive properties allowing it to bond to the target surface. The bonding layer of the present invention is not a contact responsive adhesive.
An advantage of the present invention is that the bonding layer can be solvated in a variety of activating solvents, some of which are environmentally friendly and pose less health hazard to people. These environmentally friendly solvents include, e.g., d-limonene (diterpene-based material), coconut oil ester, aliphatic hydrocarbon blends, and petroleum distillates.
Another advantage of the present invention is that the cover slip can withstand high temperature and high humidity conditions for a prolonged period of time, as further described herein, without adversely affecting the specimen. As a result of the performance, the specimen can be preserved for a longer period of time.
A tack-free bonding layer would have a tack value of less than 2, preferably 1.5 and lower, most preferably 0.5 and lower before activation. It would have little to no (i.e., less than 0.5 N/25 ohm, preferably nearly 0) adhesion to glass before activation, as measured according to ASTM D-333D, described below.
In yet another advantage of the invention, the bonding layer is initially tack-free, meaning that it has little to no adhesion to most substrates, such as the slide, the equipment parts used to perform cover slip operations, skin, and gloves until it is activated. Upon exposure to an activating solvent, the bonding layer quickly acquires tack and adheres to the specimen and slide.